Video: Adjusting substeps and solver iterations

Depending on the complexity, of and/or the level of realism required, for our MassFX simulations, accuracy may be an extremely important aspect of the simulation that we want or need to have control over. In this video we will consider two global options that will have a significant impact on the accuracy of our rigid body simulations. Do keep in mind that as a general rule, to increase the accuracy of a simulation, the number of collision calculations used to compute it also need to be increased.

This course introduces basic physics simulation principles in Autodesk 3ds Max using MassFX, a system that makes it cost effective to animate rigid body objects, cloth, and particle systems. Author Brian Bradley introduces basic concepts such as gravity, drag, volume, and density, and how Newton's Laws of Motion can help you understand the interaction of objects with these unseen forces. Using the purpose built scene, Brian walks through the tools and features of the MassFX (PhysX) system, applying the principles discussed as he goes. Along the way, discover how to combine rigid bodies and constraints, mCloth fabrics, and mParticles geometry to create fairground-style effects.

Adjusting substeps and solver iterations

Depending on the complexity, of and/or the level of realism required, for ourMassFX simulations, accuracy may be an extremely important aspect of thesimulation that we want or need to have control over.In this video we will consider two global options that will have a significantimpact on the accuracy of our rigid body simulations.Do keep in mind that as a general rule, to increase the accuracy of asimulation, the number of collision calculations used to compute it also need to be increased.

As the computational requirements for the calculations increase, so, too, does theoverall simulation time.In simulations, as in rendering, cost versus benefit will be an ongoing balancingact that we need to look at.We have already in this course discussed the importance of understanding therelationship between the animation frame rate settings in our scene and thenumber of collision calculations taken for every second of simulation time.If, as is the case in the scene, we are working with a frames-per-second settingof 24, MassFX will take 24 collision calculations, or steps, per second itself.

If however, we were to increase the substep value in our MassFX Tools dialogup to 1, well, MassFX would now make 48 collision calculations per secondinstead of the original 24.The result of the increased computation is of course a more accurate simulation.This increase in both the number of calculations per second and simulationaccuracy continues as we add more subframe sampling, or substeps, to the process.

No,w our natural inclination given these facts might be to start our simulationswith a high substep value.This, however, would be a mistake for two reasons.Firstly, as we have mentioned, the cost of increased accuracy isincreased simulation time.In a production environment, this would also equate to increased cost, whichobviously is bad for everyone expect maybe our electricity provider.The second reason is that a more accurate simulation does not always meana better-looking one.

We need to remember that as technical artists our goal is to produce a simulationthat fits the needs off our current project, one that looks good, not asimulation that is more mathematically correct.If it fits the bill using only a limited number, of or maybe even no sub stepsat all, then we should be happy about that and move on to the next task at hand.Another global setting that can improve the final quality or final accuracy ofour simulations is this Solver Iterations values. Rather than affecting thedynamic rigid bodies themselves, this option controls the number of times aconstraint solver enforces collisions in constraints during a simulation.

In some instances higher values than default may be necessary, such as when asimulation is making use of a large number of constraints, or when thetolerance for joint errors needs to be very low, such as may be the case whenworking with a ragdoll.Again just to be clear: this value works on constraints in the simulation notthe dynamic rigid bodies themselves, as has sometimes erroneously been stated.In our next video, we are going to give consideration to a third option thatcan help with accuracy in rigid body simulations, this being the Generate ShapePer Element control.

We will also look at an extremely useful tool with which we can visually debugour simulations--this being the aptly named MassFX Visualizer.

There are currently no FAQs about Creating Simulations in MassFX and 3ds Max.

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